Such measuring probes are required for measuring the thickness of layers in the hard-to-reach areas of workpieces. For example, measurements must be taken at the bottom of gear teeth surfaces or at the bottom of threads of in U-shaped grooves. The probe must indicate the correct voltages even when the probe is not completely perpendicular to the layer.
From the German Utility Pat. No. 7,336,864 it is known how to use a ball-bearing ball, half of which has been ground off, on the front surfaces of the magnetic yoke of a probe. Inside a very large solid angle, owing to the point (radial) symmetry of a spherical surface, the probe can be placed at an angle. Nevertheless, one obtains the same measurement result as when placing the probe perpendicularly.
However, if one wishes to measure at hard-to-reach spots, one would have to use very much smaller hemispheres than when measuring on plane sheet metal or other plane surfaces. If one progressively reduces the size of the system described in the German utility patent, the curvature of the surface on which the measurement is made plays a progressively smaller part. However, if one reduces the entire measuring system linearly, the output voltages become progressively smaller and one reaches the area of noise or catches interference voltages coming from the industrial plant or from medium-wave transmitters, because such probes operate in the same frequency range as medium-wave transmitters.
It is, therefore, an object of the present invention to create a probe with which one can measure on surfaces of small radius of curvature and with which one obtains output voltages which are of the order of magnitude conventional with mesuring probes and where there is no danger that interference voltages predominate. However, this object must be realized at minimum cost and measuring personnel must not be expected to require considerable retraining in comparison with the previous measuring method.